OTTAWA — Canada and Russia traded barbs at the United Nations on Thursday as Foreign Affairs Minister Stephane Dion led calls for an end to the bloody conflict in Syria.

The exchange came during a special session of the UN General Assembly, organized by Canada and supported by more than 70 countries, in which Canada hoped to ratchet up pressure on Russia and Syrian President Bashar Assad to end the five-year-old war.

Dion blasted the Security Council’s failure to end the conflict before turning his sights towards Russia and Assad. The two have a responsibility to protect civilians, he warned, before calling them “belligerents” to the conflict.

Dion called for an immediate end to airstrikes in the city of Aleppo, where Russian and Syrian government forces have conducted an unprecedented number of airstrikes in recent weeks. And he brushed aside a “pause” in the bombing instituted by Russia earlier this week.

“A short humanitarian pause, announced unilaterally, without notice and without clear parameters, does not allow the necessary aid,” said Dion.

About 250,000 people are trapped in rebel-held parts of the city, which aid convoys have not been able to reach since July. UN officials reported that water and food supplies are running dangerously low and half of those caught in the crossfire are children.

But Vitaly Churkin, Russia’s ambassador to the UN, showed no signs of backing down. Instead, he repeated past assertions that Russian and Syrian forces were fighting terrorist groups, some of which have been trained and equipped by the U.S.

Churkin went on to note that Dion had made no mention of either the Islamic State of Iraq and the Levant or other terrorist groups, and he appeared to question if Canada was committed to fighting such elements.

Syrian Ambassador to the UN Bashar Jaafari also attacked Canada, accusing it of violating his country’s sovereignty by deploying military forces inside Syria without permission.

Canadian fighter jets conducted several bombing missions against ISIL inside Syria between March 2015 and February 2016. While those warplanes have since been withdrawn, Canada still has two surveillance planes and an air-to-air refuelling aircraft operating in Syrian and Iraqi airspace.

Karam Al-Masri / AFP / Getty Images The rubble of a destroyed building following reported air strikes in Aleppo, on Oct. 17, 2016

But Dion was far from the only one to lament the Security Council’s failure to intervene or criticize Russia and the Syrian government. Diplomats from around the world echoed his concerns, as well as the idea of holding an emergency session of the General Assembly to sidestep the Security Council.

Diplomats from a number of countries also thanked Canada for organizing the session, even as they blasted the Security Council for its inaction.

In an interview before the session, Dion said Canada and other countries were expressing their “frustration” with the current situation. And while the session itself will likely turn out to be largely symbolic, “we need to try everything.”

“I think it will add to the pressure for action,” he said. “Because you will have many countries saying the same thing, accentuating the sense that inaction is unacceptable.”

Diplomats were particularly critical of Russia’s decision to veto a Security Council resolution on Oct. 8 that would have demanded an end to airstrikes and other military flights over Aleppo.

In their briefings, UN officials painted a dire picture of the situation in Aleppo. UN Secretary General Ban Ki-Moon said he had “few words left to describe the Syrian tragedy.”

Health care facilities have been “mercilessly pummelled” and “hunger has been used as a weapon,” Ban said.

BEIRUT — At least 23 civilians were killed in renewed government airstrikes on the contested city of Aleppo, Syrian activists said Sunday, as the United Nations Security Council convened an emergency meeting on the spiralling violence in Syria.

At the start of that meeting the U.N.’s top envoy to Syria accused the government of unleashing “unprecedented military violence” against civilians in Aleppo.

Staffan de Mistura said Syria’s declaration of a military offensive to retake rebel-held eastern Aleppo has led to one of the worst weeks of the 5 1/2-year war with dozens of airstrikes against residential areas and buildings causing scores of civilian deaths.

He said the offensive targeting civilians with sophisticated weapons including incendiary devices may amount to war crimes.

Medical workers and local officials reported airstrikes on neighbourhoods throughout Aleppo’s rebel-held eastern districts as an announced government offensive entered its fourth day.

The Britain-based Syrian Observatory for Human Rights reported 23 civilians had been killed by 6 p.m. and said it expects the toll to rise.

Ibrahim Alhaj of the Syrian Civil Defence search and rescue outfit said hospitals and rescuers have documented the deaths of 43 people so far.

Hospitals are overwhelmed with casualties and medical workers are expecting many of the wounded to die from a lack of treatment, according to Mohammad Zein Khandaqani, a member of the Medical Council, which oversees medical affairs in the opposition areas.

“I’ve never seen so many people dying in one place,” he said from a hospital in the city. “It’s terrifying today. In less than one hour the Russian planes have killed more than 50 people and injured more than 200.”

The Observatory, which relies on a network of contacts inside Syria, said earlier in the day that 213 civilians have been killed by airstrikes and shelling on opposition areas in and around Aleppo since a U.S.-Russian brokered cease-fire collapsed Monday evening.

De Mistura, at the Security Council meeting, warned that if the Syrian government is intent on taking Aleppo, it is going to be “a grinding” street-by-street fight where all the infrastructure in the city will be destroyed, but it won’t lead to victory.

“A so-called military solution is impossible including in Aleppo,” he stressed.

He urged the United States and Russia to go “that extra mile” and save the Sept. 9 cessation of hostilities agreement “at the 11th hour.”

Prior to the start of the U.N. meeting, British Foreign Secretary Boris Johnson said Russia should be investigated for war crimes following a Monday attack on a Syrian aid convoy that claimed 20 lives.

Johnson said that Russia’s air force may have deliberately targeted the civilian convoy on Sept. 19. Russia denies involvement and instead suggests Syrian rebels or a U.S. drone were responsible.

France’s Foreign Minister Jean-Marc Ayrault said Russia and Iran will be guilty of war crimes if they don’t pressure Syrian President Bashar Assad to stop escalating violence.

Ayrault said the emergency Security Council meeting Sunday is a “moment of truth” for the U.N.

The meeting was requested by the United States, Britain, and France, as pro-government forces extend their bombardment of the contested city of Aleppo. They are widely believed to be accompanied by Russian air strikes.

A so-called military solution is impossible.

Rebels meanwhile shelled Masyaf, a government stronghold near the central city of Hama, for the second day in a row, according to the Observatory.

Masyaf is home to a large number of Alawites, members of President Bashar Assad’s sect. Assad has rallied Syria’s minorities behind his government behind fears of the Sunni-dominated rebellion.

The U.S., Britain, and France are aligned on the Security Council against Russia and China, which back Assad in the country’s protracted war, now in its sixth year.

But a broad coalition of Syrian rebels denounced international negotiations for peace as “meaningless,” earlier Sunday.

The statement released jointly by 33 factions called on the government and Russian forces to halt airstrikes and lift sieges on opposition areas. The U.N. estimates 600,000 Syrians are trapped in various sieges enforced by the government, rebels, and the Islamic State group across the country.

“Negotiations under the present conditions are no longer useful and are meaningless,” the statement said.

The factions said they would not accept to have Russia mediate any negotiations, calling it a “partner to the regime in the crimes against our people.”

The statement was signed by some of the largest factions from across Syria but did not include the powerful, ultraconservative Ahrar al-Sham nor the al-Qaida-linked Fatah Sham Front.

Efforts to revive the truce have floundered. An airstrike destroyed a U.N.-backed humanitarian convoy Monday inside opposition territory shortly after the Syrian military announced the agreement had expired. The U.N. says the attack could amount to a war crime if proven deliberate, though it has not assigned responsibility yet. The U.S. says it believes Russian jets were behind the strikes.

Rebels Sunday retook an area in Aleppo that fell to government forces the day before, extending a punishing stalemate in the contested northern city.

The Observatory says rebels seized Handarat, a largely uninhabited former Palestinian refugee camp, early Sunday — a day after it was lost to government forces. The camp has changed hands multiple times and is largely devastated and abandoned.

The area is near Castello Road, a vital supply route to the city’s besieged rebel-held areas. Government forces seized the Castello Road earlier this year, besieging rebel-held districts where some 250,000 people reside.